Experimental Study on the Dynamics of the “Fracture–Migration” Effect in Overburden Under Dynamic Disturbance

To investigate overburden movement and three-zone development under far-field strong dynamic disturbance induced by instability of typical thick and hard overburden in western mining areas, a large-scale two-dimensional physical similarity simulation was conducted using the 11N0201 working face of Maiduoshan Coal Mine as the engineering background. Four test scenarios were designed: a baseline condition, dynamic loading, pressure-relief boreholes, and coupled disturbance. The results show that dynamic loading shortened the first weighting interval of the overburden by 45.5%, while the thicknesses of the caving zone and fracture zone increased to 15 cm and 42 cm, respectively, representing increases of 36.4% and 20.6% relative to the baseline condition. At the fully mined stage, fracture connectivity increased to 45%. A fracture intersection angle of <50°, connectivity of >40%, and abrupt aperture variation can be regarded as empirical semi-quantitative precursor indicators of a dynamic instability tendency in thick and hard overburden. By introducing prefabricated weak planes, roof pre-splitting guided the directional development of fractures and caving. Under coupled disturbance, the thickness of the fracture zone was reduced by 42.9% compared with that under dynamic disturbance alone, and the amplitude of displacement fluctuation decreased by 33.3%. These changes promoted a transition in overburden movement from an “unordered dislocation” state to a controllable state of “dynamic-disturbance-induced, directionally regulated stability”. These findings provide an experimental basis for early warning and prevention of overburden instability under far-field strong dynamic disturbance in western mining areas with thick and hard overburden.